Yep. Now imagine what would happen if each clan was limited to a few tousand pieces?
I would guess a medium sized mainbase will perform well enough and would reach about 1k pieces.
Anything reaching 10.000 is probably more of some pve or some distraction/lag build.
Speaking of dick structures - 2 my clanmates like to do anti-treb-landclaim as well. So one might blame us as well… 
technically, probably half+ would do it (would need to test how much it reduces every foundation out from center) with spray damage included. And your steelfire, brimstone and tar #'s are off. for 6676 you basically need 372130 of tar and brimstone (forgot the 5 brimstone per dragon powder, and 5 tar for final bomb). and only need 338300 steel fire.
Uhm. I think you got a few typos, but I may be wrong.
If we are speaking about 100x100 squares in need to be blown away, that results in 398 foundations. As each foundation is said to be blown by ~17 jars, we need 398*17=6766 (not 6676) jars.
However it’s true that I didnt count jars being AoE in. I guess half of bombs would suffice maybe even less. But still.
Who would do all that grind while those who blocked the damned thing will raid everyone who opposes them? I see blocking obelisks as the last move prior to raiding a big clan OR a bunch of clans. So first comes the huge grind, while nobody knows about whats to come, then the blockage and ultimately the raid.
Who is supposed to remove the obstacles? Even more if a clan means to deny their enemies any access to efficient jar-farming. (Like blocking brimstone and popular hunting grounds for thick hide.)
I think it’s most likely that people will just quit (that server).
True. Though to block an obelisk, inner fences suffice. If one doesnt want to place a ton of archers on top… 
I still like the idea of both worlds, build “anywhere” conan, but with a claim object to claim area like the feed pots. This way, people have targets they can hit to break connection spammed walls. It could be tiered as well. 5x5, 10x10, 25x25 area. And since one could not place in teh obelisk area, they would almost have to have 4 to cover their walls on each side of obelisk.
Sounds interesting.
Lets think about how that would look like? They would act like foundations (allowing buildingparts to snap to them) and only look different. Also those 5x5 to 25x25 would have no vertical value and would replace the current landclaim completely.
Those claim-buildings would have same HP as foundations of the respective tier - 5k, 50k or 100k) and possibly even include a conquest system? (This has been asked for as well - though that was months ago.) Like if you reach such a flag and can maintain a 300 second channel, ownership of that particular landclaim goes to the attacker.
Maybe building without landclaim should be possible as well, but then there is no owner - everyone would be able to destroy them or reset the timer. Great for infrastructure like maprooms, bad for griefing.